<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
<style>
    .fu{
        background-color: #ff0;
    }
    .fu>div{
        width: 100px;
        height: 100px;
    }
    .z1{
        background-color: #f00;
        position: relative;
        z-index: 1;
    }
    .z2{
        background-color: #0f0;
        position: relative;
        left: 50px;
        bottom: 50px;
        z-index: 5;
    }
    .z3{
        background-color: #00f;
    }
</style>
</head>
<body>
<div class="fu">
    <div class="z1"></div>
    <div class="z2"></div>
    <div class="z3"></div>
</div>
</body>
</html>